Process for preparation of a dyestuff sensitized photoconductive composition

ABSTRACT

WHEREIN R is alkyl of 1 to about 5 carbon atoms; and X is an anion residue. Such polymeric materials are highly effective sensitizers for organic photoconductors such as the poly(vinylcarbazoles). Process for preparation of polymeric dyestuffs of the formula:

United States Patent [1 1 Watarai et al.

[ PROCESS FOR PREPARATION OF A DYESTUFF SENSITIZED PI-IOTOCONDUCTIVE COMPOSITION [75] Inventors: Syu Watarai; Yoshio Seoka, both of Tokyo, Japan [73] Assignee: Rank Xerox, Ltd., London, England [22] Filed: Nov. 14, 1973 [21] Appl. N0.: 415,594

[52] U.S. Cl. 96/1.6; 96/l.5; 260/67.5; 260/315; 260/895 R l N [51] Int. Cl. G03g 5/06; G030 1/72 [58] Field of Search 260/315, 67.5, 895; 96/15, 1.6, 1.5 C

[56] References Cited UNITED STATES PATENTS 3,647,432 3/1972 Holstead 260/315 51 July 22, 1975 OTHER PUBLICATIONS J. Chem. Soc. ll7:l542-l550 (1920) Copisarow.

Primary ExaminerI-Ienry R. Jiles Assistant ExaminerS. D. Winters Attorney, Agent, or Firm.lames J. Ralabate; James P. OSullivan; John H. Faro [57] ABSTRACT Process for preparation of polymeric dyestuffs of the formula:

wherein R is alkyl of l to about 5 carbon atoms; and X is an anion residue.

Such polymeric materials are highly effective sensitizers for organic photoconductors such as the poly(- vinylcarbazoles).

11 Claims, No Drawings PROCESS FOR PREPARATION A F S SI IZ D IQ0 DU W comrosnflroivi i arehighly effective in these toconductiv'e mater'ials.

2. Description of t v The formation and 'development efiima eisfo me 'imaging surfaces offphoto'cond uctiveimateriails'hy" electrostat'ic means we ll known. Thebest'kno'wn of the commercial processes, more commonly knownias" xerography, involve sfofming ala'tenfelectrostatic image on the siiiface of an ima gin griiember first uniformly electrostaticallycharging the surfae e'bf'the imaging laye'rin th dark'and then exposing' this erectrostatically charged surface to a light afid shadow image. The light struck are as' 'of th 'e irr'iag'ing l ayer'a're thus rendered conductive and tl'ie elecftr osta'tic chargeselectively dissipated in these irradiated zii'teasfAftet the photoconductor .is exposed, the latentH-electrostatic image on this image bearing Surface isrenderedvisible by development-with a finely divided .coloredelectroscopic material,.known in the,art as-tonerl? This toner will be principally attracted to. those areas-onlheimage bearing surface which retain. the/electrostatiocharge and thusrforma visiblespowder imagery-U t.

The developed image can then be readorpermanently affixed tojthe ph'otoeonductof where the muging layer pot to be reu seld. This latterptactice is usually followedwith respectgto the: binder-typephotoconductive films: ejg'. Zinc oxide/insulating"resifi)'where the photoconductiveirnagirig layer i's'also'ari integral part of the'fi nishe d copy. l

' In so-called "fpl ain paper copying thelatent image can be developed on the ingsurface of areusable photoeo n'ductor oftransferredtoan'otifer surface, such as sheet of paper, 'thereaft'er' 'devel oped. When later t irriageis defveloped oii the iinag; ing surface'of a reusable'photo conductqr jt s h quently transferred toanoth'er substrate {then per manently affixed thereto. Any one of a variety 'of well known techniques" canbeused to'pernianent]y affix the toner image to the copy' she'et, "including ojvercoating with transparent fi mga a solvent oflthermal fusion of the toner particles to thELirm r't iv 'snb'tr'atelf In the abov e plain pap er copying sys e fll thelrhaterials used in the photoconduct or layef siioiild pfefereably be capable ofrapid switching-from insulative" to conductive to insulativ'e-state-inforder to'permit cyclic use of the imaging layer. Thefailure'of a material'toreturn to its relatively'insulative state prior to-the succeedingcharging-sequence.will result inan 'incr'ease in the dark decay rate of the iphotoconducto'n This phenonenon, commonly'referred to in the artas fatigue has in the past'bee n-avoidedby the-selection of photoconductive materials possessing .rapid switching capacity. Typical ofthe materials suitable for'useifi sucha rapidlycycling-imagi ng system include anthracerfe; sul fur, selenium iHIlClM mlXtUfeS, thereof ('U.S Pat.il Joi 2,297,691 )iselenium being prefrr ed because of its superior photosensitivityfi. i i

In additionto anthracene, other organic photoconductive Imaterials, most notably, poly(N- vinylcarbazole). have been the focus of increasing inlcrestiin electrophotography. US. Pat. No. 3.037.861. Until recently. neither of these organic materials. namely, anthracene or poly(N-vinylcarbazole), havereceived serious consideration asan alternative to such inorganicphotoconductors as selenium. due to fabrication difficultiesand/or therelative lack of speed and photosensitivity. The recent discovery that high loadings o 2,9,7-trinitro-9-fluronone in polyvinylcarbazoles dramatically improves the photoresponsivcness of these materials haslead to a resurgence in interest in organicphotoconductive materials, US. Pat. No.

3,484,237. Unfortunately, the inclusion of high loadings of suc;h. activators can and usually does result in phase separation of the various materials within such a composition. Thus, there will occur within such traditionally sensitized compositions, regions having in excessive activator regions deficient in activator and regions, having the proper .stoichometric relationship of activator tophotoconductor. The maximum amount of activator that may be added to most polymeric photoconductive materials without ocassioning such phase separatiori generally will not exceed in excess of about 6 to about .8 :weight percent.

One method suggested for avoiding the problems inherent in the useof such activators in conjunction with polymeric photoconductors, is the direct incorporation of, these actiy ators into the polymeric backbone of the photoconductor, US. Pat. No. 3,418,116. In this patent is disclosed the copolymerization of a vinyl monomer having anaromaticand/orheterocyclic substituent capable ,of an electron donor function with a vinyl monomer having an aromatic and/or hetcrocyclic substituent capable ofan electron acceptor function. The

spatial constraint placed upon these centers of differing electron density favors their charge transfer interaction uponphotoexcitation of such a composition. Thesesocalled ffintramolecular charge transfer complexes, more accurately designated intrachain" charge transfer arebelieved to function substantially the same as charge transfer complexes formed between small acti vator molecules and a photoconductive polymer. The fact that the electron donor function and an electron acceptor are on a common polymeric backbone does not apparently change the 11' 1r charge transfer interacti onvbut merely increases the probability of it occurring. -.U nfortunately, the preparation of such copolymers from vinyl monomers having electron donor centers and vinyl monomers having an electron acceptor center is often besehwith difficulty.

Separate and distinct from the sensitization of photoconductive materials with so-called factivator" materials is the" addition of highly colored materials (dyestuffs) to photoconductive materials for the purpose of extending the spectral range of sensitivity of the photoconductors, The same problems and limitations discussed previously withregard to the inclusion of the activators into the photoconductive materials also applies with regard to the inclusion of dyestuffs into photoconductive materials. Traditionally, such dyestuffs are prepared independent of the photoconductive material and thereafter incorporated therein.

Carbazole functional dyestuffs have been previously disclosed in the technical literature, M. Copisarow, J. Chem. Sod-T17, 1542 1550 (1920). The Copisarow teria'ls; 'A-nothe'r object o'f this invention is to provide a pro- .3 article teaches the preparation-of carbazole -blueand carbaz'ole violet dyestuff pigment The author'rcgai'ds his'p'rocess as 'a cornbinationo-fthe aldehyde and phosgeneprocesses used in the formationof the triphenylamine'series of dyes: Tradition-ally: where 'the dyestuff is" prepared independant of the phbtocondiictivc material, and thereafte rdisperse'd therein the amount of dyestuff 'c'apable of incorporation into' said photoconductor is limitedi' "It isfther'fbr, theobje'ctof this inventio'wto en-' han'cthe sensitization of orgaiiic photoconductive ma- The above and related objects" are achieved by providing a process forthe preparation of a'triaryl methane dyestuff-wherein ainixture c on'taining an organic polymeric photocoriductive material, about 2 toab out' SO ar tS weight 'N-a'lkyl-3 formylcarbazole pcr' lO O partsorganic polymericphotoconductive material and aquantit'y'bf polyph os'pho ric acid equivalentft'o about $"to about 50"times th'e weightof orgahic polymeric photo conductivematerial, is heated with agitation at a temperature ranging fromabout 't0'ab o'ut 120C for 4 whe rein-R'is an a Htyliof l toiabout 5 carbon atoms. in a solution bomprising polyphosphoric acid and an organic polymeric photoconductive material. Subsequent to theformationof the triarylmethanedyestuff, the colored polymericproducts thus obtained are separated from the acid and. thereafter. formed from a suitable sfol've n't'intoa photoconductive imaginglayer.

a p eriod'sufficient to effectformati'o'nof the desired dye stuff: The temperature at'whic'h such 'reaction is carried out will, of course, determine th"'rat at which mmaysmrra formed; It isalso-noteworthy that in the dyestu'ff formation process, t'he reaction jma y be terminat e'd prior to complete' po'lym'eri'zation' of the N aIky'T-S-fdrmylcaib aiole; In the preferred embodime rjts' of this'inventionfthe dyestuff precursor c'anbe either "N mjthyl-3=formylcarbazol or N ethyl 3 forrnyl'carbaz'ole. Any one of a'number of organic photocdnductive materials can bep'resent' in the reaction mixture during the synthesis of this'polynieric dyestuff. Typical'of such organic photoconductive materials incliide 'any cf the polyvinylcar'bazoles "(e."g.' poly(N- The dyestuff precursor compounds, namely the N- I alkyl- 3 -formyl carbazoles, which can be used in this process can betreadily prepared from commercially available materials by methods disclosed in the technical literature. Typical of the niaterialswhich are suitablein this regard include N-methyl-3-formyl carbazol e, N-ethyl-3-formyl carbazole, ,N-propyl-3-formyl .carbazole, N-butyl-3-forr nyl carbazole and N-pentyl-3- fo rmyl carbazole. The concentration of precursor compound(s) used in such synthesis is based upon the relative concentration. of acid and organic polymeric pho toconductive materialspresent in the reaction mixture. Generally, igoodresults are obtained wherein the concentratiqniQf precursor inlthereaction mixture is in the range of from about} to about 50 parts by weight precursor pe rI lOQ partslby weight organic polymeric pho .toconduCtivc materials.

a The reaction medium employed inthe condensati'onpolymeriZation of the above=materials is polyphosphoric acid. It is generally preferable that such 'ac'id be fairly concentrated. The relative concentration of such acidin-the reaction mass should'be in the range of from about 5 to 50 times the weight of organic polymeric photoconductive materials used in said synthesis.

The third essential component'of the reaction mass is an organic polymeric photoconductive material. Any of the;materialsiheretofore "described in the patent and technical literature are suitablefor use in said synthesis; Typical of the riiater'ials which can be selected as the organic polymeric photocqnductive component of the reaction mass include the polyvinylcarbazoles e.g. pbly( l\l-'vinylcarbazp le), h poly(N-ethyl -3- vinylcarbazole); poly( N-methyl-3-vinylcarbaiole )fpol- 'ytN- hyl' rv iy s i s), lp yt t y v'inylcarbazolej; poly(vinylpryeni and poly( vinylpryenal); lt is 'not believed that theorg anic polymeric photoconducti've component of thereaction mass is chemically altered during synthesis of the triaryl methane dyestuff. The organic polymeric photoconductive material and the dyestuff are, however; physically bound togetherf :during the condensation-polymerization of the precursor compound, thus,'forming a complex wherein the photoconductive ,material and the sensitize r arle intimately associated with one another.

.- Subsequent to the intimateadmixture of the above components in their proper relative proportions, the reaction mass thus-produced is agitated. and heated.

.The timesrequired 'to effect formation ofthe desired productwill vary with the temperature used in carrying out this processaand the nature .of the. product desired.

.is;.controlled by the duration of the reaction interval.

For example wher'e the polymerization condensation of the N-alkyl-3'-formyl carbazole is allowed to proceed (at C) for less than about l0'minutes, the product will predominantly comprise a triaryl methane dye (nonpolymerized) having the following structural formula:

c I wherein X 15 an anion residue Subsequent to preparation of the triaryl methane dye in the desired form(polymerized v. nonpolymerized) such materials on the conductive. substrate, preillumination of such materials in the casting solvent with activatingelectromagnetic radiation enhances the optical density of the dissolved dyestuff.

The Examples which follow further define, describe and illustrate the process of this invention. Apparatus andtechniques used in such process are presumed to be standard or as hereinbefore described. Parts and percentages appearing in such Examples are by weight unless otherwise indicated.

i l X- EXAMPLEl -V A series of dyestuff senistized photoconductivecomthe reaction is quenched by pouring the reaction mass 55 positions are prepared from poly(N-vinylcarbazole) into a large volume of distilled water. The colored polymeric products precipitate out and are separated from the aqueous medium by filtration. Subsequent to removal of these aqueous residues the colored polymeric product is purified by reprecipitation from alternate solutions of water and methanol. After the colored polymeric products have been cleansed of impurities, it can be dissolved in a suitable solvent, such as chloroform or methylene chloride, and coated on a suitable conductive substrate (aluminized mylar, conductive glass plates, aluminum, etc.). The quantity, ,Ofmaterial which is imparted to such a substrate should be sufficient to form a photoconductive imaging film having a dry film thickness in the range of from about 0.5 to about 50 microns. It has been observed,.thatprior to casting of and N-ethyl-3-formyl carbazole. The exact proportion of these materials in each of the compositions is disclosed in Table I appearing immediately after the text of this Example. In each instance, the poly(N- 6O vinylcarbazole) is initially dispersed in 50 grams polyphosphoric acid. N-ethyl-3-formyl carbazole is then added to'the dispersion while the dispersion is continuously vigorously agitated. The temperature of this dispersion is gradually increased to about 60C and there- 5 after maintained at this level for the prescribed reac- -vacuum and thereafter dissolved in a suitable solvent (e.g. chloroform or methylene chloride). In a limited number of situations (Examples VIII and IX) the casting solvent containing the polymeric composition. is subjected to preillumination with activating electromagnetic radiation whereby its opticaldensity is substantially enhanced. Subsequent to this preillumination treatment the solution containing the colored polymeric solids is cast or coated on an appropriate conductive substrate. The quantity of colored polymeric materials that is transferred to such substrates is sufficient to form a substantially uniform film having a thickness in the previously prescribed range. Any' of the conductive substrates traditionally used in the preparation of el'ectrophotographic imaging members are suitable.

TABLE I Example Poly( N-vinyl N-ethyl- Reaction Absorption No. carbazole) 3-formyltime peak in carhazole (minutes) nanometers (g) (g) (nm) l, 2 0.] l 602 ll 2 0.] 609 Ill 2 0i 6() 609 IV 2 0.2 60 610 V 2 0.4 610 Reaction temperature 60C in Examples l V.

EXAMPLE VI' About 0.2 grams of the colored polymeric composition of Example I is dissolved in 6 milliliters of methylene chloride and thereafter coated on a conductive paper substrate such that its dry film thickness is about 15 microns. Subsequent to curing of this polymer coating, the resulting imaging mernber is processed in a standard electrophoto'grap'hic imaging system. The

source of illumination used in projecting the image pattern on the corona sensitized polymeric coating is a tungsten lamp. The amount of exposure required to give what was deemed to be an image of good quality is 70 lux. seconds.

EXAMPLE VII (pursues n1pad EXAMPLEVII The procedures of Example VI are repeated with the colored polymeric composition of Example Ill. The amount of exposure required to obtain an image comparable to that of Example I is 53 lux. seconds. The action spectrum for the material used in preparation of the imaging layer ofthe imaging member used in this Example is shown in FIG. 1. r

EXAMPLE Vlll' About 2 grams of the colored polymeric composition of Example lVis dissolved in about 1 milliliter of methylene chloride and the resulting solution subsequently irradiated from adistance of 30 centimeters with a fluorescent lamp (20 watts). The effects of such irradiation on a sample not having received such irradiation and samples irradiated for five minutes and 20 minutes respectively are shown in Table II.

TABLE ll Sample No. Time of irradiation An amount of correct (minute) exposure for picture image (lux. second) .A 0 51 B I 5 r 47 C 20 44 It is clear that irradiation of the colored polymeric material prior to coating on the conductive substrate improves the sensitivity of such material to activating electromagnetic radiation.

EXAMPLEQIX A About'O.l grams of the polymeric composition of Example IV and about 0.1 grams of poly(N- vinylcarbazole) are dissolved in 6 milliliters of methylene chloride. The resulting solution is subjected to irradiation in a manner similar to that of Example IX. Following irradiation, a conductive paper substrate is coated with said solutionr'Sufficient polymeric materials are transferred to the paper to provide a photoconductive imaging layer having a dryfilm thickness equal to about 15 microns. A comparative evaluation of the sensitivity of an irradiated sample with a non-irradiated sample are shown in Table III.

TABLE III Sample No. Time of irradiation An amount of (minute) correct exposure 1 for picture image (lux. second) D t O 68 E l0 5] (m n ."Len-gth' CHO wherein R is alkyl of 1 to carbon atoms, said process comprising:

a. providing a mixture containing (i) organic polymeric photoconductive material (ii) about 2 to 5 meric 3. The process of claim 1, wherein the organic polymeric photoconductive material is poly(3- vinylcarbazole).

4. The process of claim 1, wherein the organic polyphotoconductive material is poly(2- vinylcarbazole).

5. The process of claim 1, wherein the organic polymeric photoconductive material is poly(vinylpryene).

6. The process of claim 1, wherein the organicpoly-.

meric photoconductive material is poly(vinylpyrenal).

7. The process of claim I, wherein the compound of the above structural formula is N-methyl-3-formyl carbazole.

8. The process of claim l,lwherein the compound of the above structural formula is N-ethyl-B-formyl carbazole.

9. The process of claim 1, wherein heating of the mixture proceeds for an interval sufficient to produce a composition wherein the predominent component is about 50 parts by weight of a compound of the triaryl methane dyestuff of the formula above formula per 100 parts organic polymeric photoconductive material, and (iii) a quantity of polyphosphoric acid equivalent to about 5 to about times the weight of organic polymeric photoconductive material in the mixture; and

b. heating said mixture at a temperature in the range of from about 20 to about 120C for an interval sufficient to effect condensation polymerization of the compound of the above formula to the extent desired. 2. The process of claim 1, wherein the organic polymeric photoconductive material is poly(N- vinylcarbazole).

enhance its optical density.

Page 1 of 2 UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,895, 945

DATED July 22, 1975 I INVENTOR(S) Syu Watarai et al it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 52, insert quotations around plain paper to make it read "plain paper".

Column 1, line 53, --prefereably-- should be "preferably".

Column 2 line ll, ---2,4,7trinitro9fluonone-- should be 2,4,7-trinitro-9-fluorenone".

Column 3, line 2, -pigment-- should be "pigment."

Column 4, line 1, omit the period after atoms.

Column 4, line 27, -condensationpolymerization should be "condensation-polymerization" Column 4, line 44, poly(vinylpryene)-- should be "poly(vinylpyrene).

Column 4, line 45, -poly(vinylpryenal)-- should be "poly(vinylpyrenal) Column 6, line 53, -senistized should be "sensitized".

Column 10, line 18, -predominentshould be "predominant".

Page 2 of 2 UNITED STATES PATENT AND TRADEMARK OFFTCE QERTTFICATE 05F CORRECTIQN PATERT NO. 3, 95,945 DATED July 22, 1975 INVENTORAS) Syu Watarai et al It is certified that error appears in the ab0veidentified patent and that said Letters Pai'eniare hereby corrected as shown below:

Column 10, line 48, after the words "triaryl'methahedyestuff of the formula, insert the following formula 3 :N g C 4.x X l X c X l X- Signcd and Scaled this fourth Day Of N0 vember19 75 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN (ummissiuncr uj'Parems and Trademarks Attesn'ng Officer 

1. A PROCESS FOR PREPARATION OF A DYESTUFF SENSTIZED PHOTOCONDUCIVE COMPOSISTION FROM AN ORGANIC POLYMERIC PHOTOCONDUCTIVE MATERIAL, POLYHOSPHORIC ACID AND A COMPOUND OF THE FORMULA
 2. The process of claim 1, wherein the organic polymeric photoconductive material is poly(N-vinylcarbazole).
 3. The process of claim 1, wherein the organic polymeric photoconductive material is poly(3-vinylcarbazole).
 4. The process of claim 1, wherein the organic polymeric photoconductive material is poly(2-vinylcarbazole).
 5. The process of claim 1, wherein the organic polymeric photoconductive material is poly(vinylpryene).
 6. The process of claim 1, wherein the organic polymeric photoconductive material is poly(vinylpyrenal).
 7. The process of claim 1, wherein the compound of the above structural formula is N-methyl-3-formyl carbazole.
 8. The process of claim 1, wherein the compound of the above structural formula is N-ethyl-3-formyl carbazole.
 9. The process of claim 1, wherein heating of the mixture proceeds for an interval sufficient to produce a composition wherein the predominent component is triaryl methane dyestuff of the formula
 10. The process of claim 1, wherein heating of the mixture proceeds for an interval sufficient to produce a composition wherein the predominent component is a polymeric triaryl methane dyestuff of the formula wherein X is an anion residue and R is as previously defined
 11. The process of claim 1 wherein a solution of the polymeric products of step (b) is exposed to activating electromagnetic radiation for a duration sufficient to enhance its optical density. 